This invention relates to apparatus for determining the surface characteristics (surface topography) of an article, and, in particular, apparatus for determining the surface topography of a substantially flat article by means of a concentrated light beam.
At present there are several forms of apparatus suitable for determining the surface characteristics of an article. One of the most commonly utilised of these involves the use of a stylus which is drawn across the surface of the article at a constant speed. This apparatus is very sensitive, and because of the physical way in which it operates is very susceptible to wear induced inaccuracy. This necessarily implies that there is a relatively large amount of maintenance involved with the use of this type of apparatus.
It should also be noted that the following problems are also encountered in the use of a stylus to determine the surface characteristics:
In order to achieve an accurate determination it is essential that the surface of the article under test is level. Therefore, a large amount of time and effort can be involved in setting up the equipment and article under test; PA0 In order to ensure uniformity within the results, due to the fact that stylus machinery provides an absolute measuring device, it is important that the device be operated at a fixed temperature; PA0 In order to obtain usable results the stylus has to be drawn across the surface of the article at a very slow speed. In fact the stylus could take 30 seconds to traverse 100 mm of the surface of the article under test; and PA0 The stylus equipment is very prone to inaccuracy, because of its highly sensitive nature, caused by dirt particles and scratches in the surface of the article. This means that in order to minimise these errors the equipment and articles under test have to be cleaned thoroughly on a regular basis, or, alternatively, the apparatus operated in an expensively created dirt free environment. PA0 a concentrated light beam source; PA0 scanning means to deflect the light beam from the source so as to produce a line scan with the beam; PA0 a first lens means to collimate the light beam of the line scan; PA0 locating means to locate the substantially flat article in relation to exposure means provided on the locating means and to enable a section of the surface of the article to be exposed to the collimated light beam; PA0 a grating of constant spacing through which the portion of the collimated light beam reflected by the surface of the article on the locating means is caused to pass; PA0 a second lens means to focus the collimated light beam passing through the grating onto a sample detector means which generates a signal indicative of the intensity of the light hitting it; and PA0 means to generate a base reference signal; wherein the signal from the sample detector means and the base reference signal are processed, which processing may include filtering, by a microprocessor to provide an indication of the surface characteristics of the article. PA0 a concentrated light beam source; PA0 scanning means to deflect the light beam from the source so as to produce a line scan with the beam; PA0 a first lens means to collimate the light beam of the line scan; PA0 locating means to locate the substantially flat transparent article in relation to exposure means provided on the locating means and to enable a section of the surface of the article to be exposed to the collimated light beam; PA0 a grating of constant spacing through which the portion of the collimated light beam reflected by the surface of the article on the locating means is caused to pass; PA0 a second lens means to focus the collimated light beam passing through the grating onto a sample detector means which generates a signal indicative of the intensity of light hitting it; and PA0 means to generate a base reference signal; PA0 generating a concentrated light beam and directing this against a scanning means so that the beam is caused to mark out a cyclically repeatable linear scan; PA0 collimating the light beam; PA0 impinging the collimated light beam against the surface of the substantially flat article so that the collimated light beam is divided into a reflected portion and a portion which passes into the article; PA0 passing the reflected portion of the light beam through a grating, and then a lens means to focus the light passing through the grating onto a light detector which emits an electrical signal indicative of the intensity of light hitting the light detector; PA0 generating a base reference signal; PA0 processing the electrical signal and the base reference signal, including filtering out unwanted signals, in a microprocessor to generate an indication of the surface characteristics of the surface.